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ADVANCED COMMUNICATIONS & SENSING

DATASHEET

SX8124

24 hours timer synchronized on 50/60Hz mains

ACS - Revision 2.4

October 2010

© Semtech Corp.

APPLICATION EXAMPLES

11

Complete application schematics

The circuit can be directly powered from the mains through a diode bridge and a resistor as long as the

supply voltage is limited at ~1.2V by diodes or similar devices. The choice of the resistor that limits the supply

current must be made so that it delivers enough current for the system to supply the IC and any other device

that is connected to that supply, but the resistor must be large enough to limit the current in sleep mode (120

kOhm will limit power dissipation below 0.3W on a 220V network).

The RC filter on the power supply is there to reject 100 Hz or 120 Hz variations.

The phase detector is used to increase the precision on the 24 hours counter. It is recommended to protect

the pin with external diodes. The filter on the phase detector is there to reject high frequency perturbations

(several kHz) but must let the 50 Hz or 60 Hz go through with limited attenuation.

The timer element is a potentiometer. The total resitivity of the potentiometer must be low enough to avoid

sensitivity to the DURATION pin impedance (> 500 kOhm) and high enough to limit current drift current. The

voltage applied on the potentiometer is 1/100 of the voltage applied on the resistor that protects the supply

voltage of the chip, therefore the current through these resistors will be in the same ratio if they have the

same value.

The power element (either a resistove heater for a diffuser or a motor for a ventilator) will be controlled

through an NPN transistor.

Figure 18. Application schematics with low-power sleep mode (below 0.3 W)

200 V supply

15 kOhm

11 W Heater

1.5 – 2.0 V supply

25 mA

91 kOhm

200V

3.9 MOhm

1.2 V

1.5 mA

1 kOhm

500 uA

MSPA44

W < 300 mW

IC < 300 mA

B = 50

VC < 300 V

VB < 6V

50 uA

PHASE

DURATION

VSS

VDD

OUT

NOUT

LED

START

SX8124

ADC

DEBOUNCE

SYNC

BURST GEN

91 kOhm

200V

0Ohms